How to use
- 1Pick the race you ran (1500 m to marathon, or enter another distance in km).
- 2Type your finish time, e.g. 50:00 or 1:52:30.
- 3Compare the Riegel and VDOT predictions from 1500 m up to the marathon.
- 4Use the E, M, T, I and R paces to plan your training.
Riegel formula and the VDOT model
Pete Riegel’s formula (1977) scales a race time to another distance with T2 = T1 × (D2 ÷ D1)^1.06; the 1.06 exponent captures how much you slow down as races get longer. Jack Daniels’ VDOT uses the Daniels–Gilbert equations (1979): one for the oxygen cost of running at a given speed and one for the share of VO2max you can hold for a given time. A 40:00 10K gives a VDOT of about 51.9 and a 50:00 10K about 40.0. The tool solves those equations for each distance, so the VDOT column matches Daniels’ published tables to within a few seconds.
Training paces from your VDOT
E (easy) pace is roughly 59–74% of VO2max and should make up most of your weekly mileage. M is your predicted marathon race pace. T (threshold) is set at 88% — sustainable for about an hour in a race, used for 20-minute tempo runs or cruise intervals. I (interval) at about 97.5% is for 3–5 minute repeats, and R (repetition) at about 105% is for short, fast 200–400 m reps with full recovery. The 400 m column helps on the track.
How accurate are marathon predictions?
Both models assume you are equally trained for the target distance. A 10K time predicts the marathon well only if you have done the long runs and weekly volume; many recreational runners finish 5–15 minutes slower than predicted in their first marathon. Use a recent result (within 6–8 weeks) from a flat course in normal weather. A half marathon predicts the marathon far better than a 5K does.
Frequently asked questions
How do I predict my marathon time from a half marathon?
With Riegel, multiply your half marathon time by 2^1.06 ≈ 2.085. A 1:45:00 half predicts about 3:38:55. VDOT gives a similar figure; first-time marathoners often add a few minutes.
What is VDOT?
VDOT is Jack Daniels’ performance score: the VO2max your race result implies under his running-economy assumptions. It is not a lab VO2max, but it is consistent across distances and gives you training paces.
Why do Riegel and VDOT give different times?
They use different models. Riegel applies one fixed exponent; VDOT models oxygen cost and how long you can hold a share of VO2max. They agree closely near the race you entered and drift apart for very different distances.
What VDOT do I need for a sub-3-hour marathon?
About VDOT 54, which predicts roughly 2:58:40 — equivalent to about 38:40 for 10K or 18:40 for 5K.
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